Breathing apparatus of the above-described type is known, for example, from U.K. Patent Specification No. 2170409A. This known apparatus includes a gas circuit means incorporating various valves and throttles whereby pulses of air or oxygen can be supplied to the patient on a cyclic basis. It also includes a switch whereby, instead, gas can be supplied to the patient on a continuous basis, the gas circuit means being by-passed.
In known breathing apparatus of the type in question, the gas control circuitry is usually embodied as a control module and a hand piece connected to the control module by a length of flexible tubing. All adjustments are effected at the control module, requiring the user to free at least one hand from the hand piece, which during use has connected to it a face mask which has to be hand held to seal around the patient's mouth and nose.
It is an object of the present invention to provide improved breathing apparatus for supplying breathable gas to a patient.
The invention
According to the invention, there is provided breathing apparatus for supplying air or oxygen to a patient, comprising a housing adapted to be hand held, a gas inlet on the housing, a gas outlet on the housing, gas circuit means within the housing, a switch on the housing whereby gas is either automatically supplied by the circuit means to the gas outlet on a cyclic basis or is supplied continuously to a manually operable valve in the housing, and a manually operable member, preferably a trigger, on the housing for controlling the supply of gas to the outlet through the manually operable valve.
This apparatus has the advantage that, in use, with the face mask attached to the gas outlet on the housing, all adjustments and operations of the apparatus can be carried out with the fingers substantially without relaxing the hands holding the face mask in position. In particular, the trigger can be operated to cause cycling of the gas supply under manual control, for exaample in sympathy with manual cardiac massage.
The hand held instrument in accordance with the invention can be made relatively small and light, for example having dimensions of about 110 mm by 65 mm by 51 mm and weighing about 250 gms, and this is in part made possible by improvements in the gas control circuitry, as compared, for example, with that described in U.K. Patent Specification No. 2170409A.
Preferably the gas flow rate to the patient is controlled by a first adjustable throttle and the periodicity of the cycle is controlled by a second adjustable throttle, the two throttles being combined into a coaxial assembly of inner and outer throttle elements of which the inner throttle element is carried by the outer throttle element.
The throttle elements preferably comprise inner and outer throttle needles adjustable within a fixed sleeve. The outer throttle needle, which is hollow, and preferably controls the gas flow to the patient, is adjustable within the fixed sleeve by means of cooperating screwthreads, whilst the inner throttle needle is in screwthreaded engagement with the outer needle to control the cycle periodicity. Thus, while the cycle periodicity is independently adjustable, adjustment of the gas flow rate to the patient also automatically adjusts cycle timing. This is convenient to enable the provision of an adult/child control on the instrument. Adjustment of the control towards the child setting reduces the gas flow rate to the patient and simultaneously increases the cycle periodicity.
The gas circuit means preferably includes a main valve which produces the gas cycling effect. This main valve has a main gas inlet and a gas outlet from which gas passes to the flow rate/timing throttle means, a secondary gas inlet receiving from the throttle means a proportion of the gas flowing to the patient which is dependent on the setting of the timing needle, and a spring loaded valve member which is gradually driven by build-up of gas pressure at the secondary inlet to a position in which it occludes the main gas inlet, whereupon flow of gas to the throttle means ceases, gas bleeds back from the secondary inlet towards the throttle means, and the valve member is restored eventually to re-open the main inlet. Advantageously, this arrangement of the main valve obviates the need for a gas reservoir, for example as described in U.K. Patent Specification No. 2170409A.
In a preferred instrument, gas enters the inlet to the housing and passes to a manual/auto switch, preferably after passing through an adjustable pressure regulator, the manual/auto switch directing the gas either to the trigger operable manual valve or to the main inlet of the above-described main valve of the gas recycling circuit.
In addition to a pressure relief valve at the gas flow outlet to the patient, the apparatus preferably includes a respiratory assist valve which is operable, if the patient attempts to inhale during a gas-off phase of a cycle, immediately to relieve pressure at the secondary inlet of the main valve thereby at once to initiate a gas-on phase.